Ultrasound pulse echo method and apparatus for determining acoustic velocity of materials

ABSTRACT

A method and apparatus for determining directly the acoustic velocity cm of a material from the comparison of the ultrasonic pulse echoes obtained from the material positioned on the bottom surface of a fluid bath container with the ultrasonic pulse echoes received from the bottom of the bath container with the material removed therefrom. A cathode ray display apparatus incorporating an expandable pusle echo time base and a fixed calibrated acoustic velocity scale are employed for a direct reading from the scale of the acoustic velocity of the material.

Ute States Patent 1 I111 3,746,121

Niklas [451 July 17, 1973 i 1 ULTRASOUND PULSE ECHO METHOD AND APPARATUSFOR DETERMINING ACOUSTIC VELOCITY OF MATERIALS Ludwig Niklas, 5023Lovenich Bei, Cologne, Germany Filed: Oct. 14, 1970 Appl. No.: 80,597

Inventor:

Foreign Application Priority Data Oct. 24, 1969 Germany P 19 53 567.2

[1.8. CI 181/.5 AP, 340/3 C, 340/5 S Int. Cl G015 9/66, H04b 11/00 Fieldof Search 181/.5 AP; 340/.5 S,

References Cited UNITED STATES PATENTS Kokesh 340/5 S PrimaryExaminerBenjamin A. Borchelt Assistant Examiner-J. V. DoramusAtt0rney-Harry E. Aine I57] ABSTRACT A method and apparatus fordetermining directly the acoustic velocity c of a material from thecomparison of the ultrasonic pulse echoes obtained from the materialpositioned on the bottom surface of a fluid bath container with theultrasonic pulse echoes received from the bottom of the bath containerwith the material removed therefrom. A cathode ray display apparatusincorporating an expandable pusle echo time base and a fixed calibratedacoustic velocity scale are employed for a direct reading from the scaleof the acoustic velocity of the material.

6 Claims, 2 Drawing Figures ULTRASOUND PULSE ECHO METHOD AND APPARATUSFOR DETERMINING ACOUSTIC VELOCITY OF MATERIALS BACKGROUND OF THEINVENTION Based on known physical laws, conclusions with respect tomaterial properties, such as Youngs modulus, shear modulus, and Poissonsratio, can be drawn from the materials acoustic velocity and, for thispurpose, it is necessary to determine the acoustic velocity of suchmaterials. It is commonly known to determine the acoustic velocity byultrasound using the pulse-echo method and measuring the transit time ofthe pulse through the material, the acoustic velocity at known thicknessof the product resulting as the quotient from thickness and transittime. But this requires carrying out two different measurements insequence, firstly to gauge the thickness of the product and then tomeasure the sound transit time in the material. Deviations from accuracyof either measurement can influence the sensitivity of the wholemeasurement.

It is also known to use quartz standards or liquidfilledinterferrometers or other transit time standards to increase theaccuracy of the transit time measurement.

BRIEF SUMMARY OF THE PRESENT INVENTION The present invention relates toan improved method and apparatus for making acoustic velocitymeasurements, especially by ultrasound, of material samples bycomparison of their typcial sound propagation velocity with that of aknown substance, preferrably a fluid.

The present invention simplifies acoustic velocity measurements bymeasuring transit times only instead of gauging mechanically thethickness and additionally measuring the transit time, and thus speedingup the measurement. In accordance with the present invention there isprovided in front of the luminous screen of an associated cathode raytube a scale standardized in acoustic velocity and arranged so that itszero graduation is positioned in coincidence or alignment or can beadjusted to this position with the entry echo pulse or indication of themeasured material sample on the CRT screen, and its graduationcorresponding to the acoustic velocity of the liquid positionedcoincident with the backwall echo indication of the material sample.

The method for making acoustic velocity measurements in accordance withthis invention provides placing the sample on the tank bottom andacoustically radiating it at right angles, producing the abovementionedcoincidence or alignment adjustment by time base scale expansion of thepulse-echo apparatus, then removing the sample and reading directly onthe velocity scale the echo value from the tank bottom as the acousticvelocity value of the sample.

The simplified method of the present invention comprises first measuringthe transit time of the sound pulse in the sample material to be testedand then the transit time of the sound pulse in a fluid whose acousticvelocity is known with great accuracy as, for example, water. It isimportant for this method to utilize a travel distance in the fluidequal to the material thickness by removing the sample after the transittime measurement has been taken in the sample. This assures that thetravel distance in the sample is exactly equal to the travel distance inthe fluid which is employed for the measurement. The transit time in thematerial results from the time difference between the instant of soundentry into the material and the backwall echo from the material.

Thus, the instant of entry is clearly fixed as a value on the time baseof the luminous pattern of the cathode ray tube. The associated transittime for the equal fluid distance results from the diflerence betweenthis same fixed instant and the echo from the tank bottom, viz. as ameasurement of an identical distance whose associated travel time,however, is longer when its acoustic velocity is lower than that of thematerial under test. With c, representing the acoustic velocity of themate rial under test, 0, that of the liquid, t, the transit time in thematerial, and t, the transit time in the equal fluid distance, then,owing to the equal length of the travelled distance,

0,, t, c; t,, and consequently c,, (t,/t,,,) c,

The quotient t,{t,,, is developed from the transit time measurementaccording to the invention and, by multiplication with the acousticvelocity c, of the fluid, results in the acoustic velocity c,, of thematerial, so that reading of the time values and multiplication by theacoustic velocity is advantageously omitted and a direct readout of c ispossible.

Another embodiment of the inventon provides producing a marker pulsewhich is variably delayed in relation to the initial pulse and which issuperimposed on the CRT screen in coincidence with the echo from thetank bottom prior to the measurement, and then to read the acousticvelocity of the material without removing the material sample. Anotherfeature of this invention provides aligning the entry echo automaticallywith the zero scale graduation, for example by a commonly known devicefor automatically starting the time base by the first echo orreflection. In addition, the invention may also be realized by measuringand storing the transit time value between the entry echo and the markerpulse, then dividing by the transit time value between entry echo andbackwall echo from the material sample, and multiplying the result bythe known acoustic velocity value of the liquid, the final result beingindicated or printed. t

DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS Acontainer such as a tank 1 is filled with a liquid such-as water andsample material 4 is placed on the bottom 2 of the tank. This sample isacoustically radiated by a pulse from an ultrasound probe 3perpendicularly to the bottom 2. The sample 4 may be of steel, aluminum,or other metal, plastic, glass, or a ceramic compound. The sound traveldistance in the material 4 is s. On the luminous screen 9 of a cathoderay tube which is fragmentarily represented in FIG. 2, the initial pulse5 from probe 3 isdrawn on the time base 50. The sound entry into thematerial 4 is represented by the entry or front surface echo pulse 6,whereas the echo pulse 7 from the sample material backwall appearsspaced from the latter. The echo 8 from the tank bottom obtained afterthe sample has been removed appears on the time base displaced to theright, provided that the acoustic velocity in the fluid is lower thanthat of the material of the sample. A transparent film is placed overthe luminous screen 9 with at least one scale 11 calibrated in acousticvelocity.

When the sample 4 is inserted and the probe 3 is excited, the entry echo6 is displayed on the luminous screen due to the sound beam impinging onthe surface 411. This is represented by the point P in FIG. 2. The pointP represents the pertinent backwall reflection echo 7 from the materialbottom 4b. The transit time between pulses 6 and 7 is t,,,.

After the sample 4 is removed from the tank and the probe 3 againactivated, the echo 6 does not appear, of course, but the location ofthe echo signal 6 obtained previously may be fixed on the transit timescale by a mark or the like at the point P Since the tank bottom 2coincides with the sample bottom 4b, in both cases the same traveldistance s (FIG. 1) is measured, the point P representing the tankbottom reflection pulse appearing at the right in FIG. 2 due to thelonger transit time t,.

Now, the zero index of the scale 11 is made to coincide with the linerunning to entry echo 6, i.e., the points P and P The scale 11 of thedial 10 is calibrated and is fixed. The value of the acoustic velocity cof the sample 4 cannot be determined from FIG. 2

by a simple projection of the backwall echo 7 on the scale 11, sincet,,,, t, or 't, t,,, can indeed be measured on the time base, but not t,t,,,. This value (c,,,,,) may be obtained in accordance with thisinvention by spreading (or expanding) the time base scale 5a of thepulse-echo apparatus until the backwall echo 7 from the material iscoincident with the graduation on scale 1 1 corresponding to theacoustic velocity of the liquid. This scale mark c, is demonstrated on adash scale graduation below the scale 11.

Another simplified embodiment of the method uses a marker pulse which isdelayed in time relative to the initial pulse 5 by a settable amount,this pulse being indicated as mark 12 shown in FIG. 2. Like the soundechoes, the marker pulse is superimposed along the time base on the CRTscreen 9, and the marker 12 is set to coincide with the bottom echo 8from the tank 1 before inserting the material sample 4. After thematerial sample has been inserted, this marker 12 appears on the CRTscreen beside the entry echo 6 and the backwall echo 7. When the entryecho 6 is aligned with the zero scale graduation of the scale 1 1,either by hand or by means of an automatic device, and the backwall echo7 moved to the value of the acoustic velocity of the fluid, c,, byexpanding the time base of the pulses, the mark 12 of the marker pulseindicates on scale 11 the acoustic velocity of the material, sample. Theentry echo 6 from the sample 4 may be automatically made to coincidewith or to be aligned with the zero scale graduation of the scale 11 byuse of a commonly known device which starts the base line in response tothe first reflection. i

The above described method can be further simplified by utilizing acomputer (not shown), which stores the entry echo-to-marker pulsetransit time, divides it by the entry echo-to-backwall echo transittime, and multiplies the result by the advance keyed-in value of theknown acoustic velocity c, of the liquid, and indicates or prints theoutcome of the calculation, namely the acoustic velocity c,,..

What is claimed is:

l. The method for determining the acoustic velocity of a sample materialcomprising the steps of irradiating the sample material on the bottom ofa container of fluid which has a known acoustic velocity with anacoustic pulse to obtain both a pulse echo from the entry surface of thematerial and a pulse echo from the backwall of the material on a timebase, irradiating the container fluid with another acoustic pulse withthe sample material removed from the bath to obtain an echo pulse fromthe bottom surface of the container on said time base, aligning the zerovalue graduation of an acoustic velocity scale with the entry surfaceecho pulse on the time base, expanding the time base until the backwallecho pulse coincides with the graduation on the acoustic velocity scaledesignating the known acoustic velocity of the fluid, and obtaining theacoustic velocity reading of the material from the acoustic velocityscale at the position of the bottom echo pulse.

2. The method as claimed in claim 1 comprising the step of generating amarker pulse delayed a selected time from the initial acoustic pulse,the marker pulse being made to coincide on said time base with saidbottom echo pulse, said time base being expanded so that said backwallecho pulse on said time base coincides with said fluid acoustic velocitygraduation on said scale, said marker pulse on said expanded time basecoinciding with the acoustic velocity graduation of said material onsaid scale.

3. The method as claimed in claim 2 including the step of determiningthe transit time between the entry echo and the marker pulse, dividingthis value by the transit time between the entry echo pulse and backwallecho pulse, and multiplying the result by the known acoustic velocity ofthe fluid.

4. Apparatus for determining the acoustic velocity of I a samplematerial comprising means for irradiatingthe sample material on thebottom of a container of fluid which has a known acoustic velocity withan acoustic pulse to obtain both a pulse echo from the entry surface ofthe material and a pulse echo from the backwall of the material on atime base, said means operating to irradiate the container fluid withanother acoustic pulse with the sample material removed from the bath toobtain an echo pulse from the bottom surface of the container on saidtime base, means for aligning the zero value graduation of an acousticvelocity scale with the entry surface echo pulse on the time base, andmeans for expanding the time base until the backwall echo pulsecoincides with the graduation on the acoustic velocity scale designatingthe known acoustic velocity of the fluid, the acoustic velocity readingof the material being obtained from the acoustic velocity scale at theposition of the bottom echo pulse.

5. Apparatus as claimed in claim 4 including means for displaying thepulses along said time base on a cathode ray screen, said velocity scalebeing superimposed on said screen such that said pulses may be alignedwith selected graduation along said scale.

6. Apparatus as claimed in claim 5 wherein said scale is provided with agraduation at the point of the acoustic velocity of said fluid.

1. The method for determining the acoustic velocity of a sample materialcomprising the steps of irradiating the sample material on the bottom ofa container of fluid which has a known acoustic velocity with anacoustic pulse to obtain both a pulse echo from the entry surface of thematerial and a pulse echo from the backwall of the material on a timebase, irradiating the container fluid with another acoustic pulse withthe sample material removed from the bath to obtain an echo pulse fromthe bottom surface of the container on said time base, aligniNg the zerovalue graduation of an acoustic velocity scale with the entry surfaceecho pulse on the time base, expanding the time base until the backwallecho pulse coincides with the graduation on the acoustic velocity scaledesignating the known acoustic velocity of the fluid, and obtaining theacoustic velocity reading of the material from the acoustic velocityscale at the position of the bottom echo pulse.
 2. The method as claimedin claim 1 comprising the step of generating a marker pulse delayed aselected time from the initial acoustic pulse, the marker pulse beingmade to coincide on said time base with said bottom echo pulse, saidtime base being expanded so that said backwall echo pulse on said timebase coincides with said fluid acoustic velocity graduation on saidscale, said marker pulse on said expanded time base coinciding with theacoustic velocity graduation of said material on said scale.
 3. Themethod as claimed in claim 2 including the step of determining thetransit time between the entry echo and the marker pulse, dividing thisvalue by the transit time between the entry echo pulse and backwall echopulse, and multiplying the result by the known acoustic velocity of thefluid.
 4. Apparatus for determining the acoustic velocity of a samplematerial comprising means for irradiating the sample material on thebottom of a container of fluid which has a known acoustic velocity withan acoustic pulse to obtain both a pulse echo from the entry surface ofthe material and a pulse echo from the backwall of the material on atime base, said means operating to irradiate the container fluid withanother acoustic pulse with the sample material removed from the bath toobtain an echo pulse from the bottom surface of the container on saidtime base, means for aligning the zero value graduation of an acousticvelocity scale with the entry surface echo pulse on the time base, andmeans for expanding the time base until the backwall echo pulsecoincides with the graduation on the acoustic velocity scale designatingthe known acoustic velocity of the fluid, the acoustic velocity readingof the material being obtained from the acoustic velocity scale at theposition of the bottom echo pulse.
 5. Apparatus as claimed in claim 4including means for displaying the pulses along said time base on acathode ray screen, said velocity scale being superimposed on saidscreen such that said pulses may be aligned with selected graduationalong said scale.
 6. Apparatus as claimed in claim 5 wherein said scaleis provided with a graduation at the point of the acoustic velocity ofsaid fluid.